The present invention relates to a novel ceramic material of hydroxyapatite, which is useful as a substitute material for bones in the fields of surgery and orthopedics or the filling material in a cavities of bones in the fields of dentistry and oral surgery and a process for producing the novel ceramic material. The ceramic material of hydroxyapatite of the present invention is a ceramic material of hydroxyapatite with continuous and two-dimensional pores, which is excellent in its affinity with and an adhesion to the newly formed bones by virtue of having continuous passages in two-dimensional directons, and has the strength necessary to be used as a substitute material for bones by virtue of having a layer of highly compressed ceramic.
Hydroxyapatite has been known as one of the constituent components of bones and teeth and because it is excellent in an affinity with a living body and is not injurious to a living body, hydroxyapatite has been expected as the prosthetic material in a lost part or a cavity of the bone accompanying the fracture of a bone and the erosion of the bone tumor, thus many studies have been carried out concerning the medical use of hydroxyapatite.
Of the studies, porous hydroxyapatite has been proposed as the material which accelerates an activation of the osteophagocytes and the osteoanagenesis cells and is easily able to be fixed into one body with a bone of the host. For instance, in Japanese Patent Application Laid-Open (KOKAI) No. 57-119,745/1982, a three-dimensionally porous prosthetic material of the mean diameter of the internally continuous openings of 0.1 to 8 mm and of the porosity of not less than 60% has been disclosed and in Japanese Patent Application Laid-Open (KOKAI) No. 60-16,879/1985, a porous material in which the internal openings of a diameter of 1 to 600 .mu.m have been connected to outside space by capillary vessels of a diameter of 1 to 30 .mu.m has been proposed.
However, when a material is made porous, the reduction of its strength is generally unavoidable and such a material is not necessarily satisfactory in the point of porous hydroxyapatite which is excellent in an affinity with a living body and has a practically reliable mechanical strength.
As a result of the present inventor's earnest studies, while considering the above situations, for developing an implant material which is excellent in an affinity with and an adhesion to the newly formed bone and is high in strength, it has been found by the present inventors that the porous hydroxyapatite which is obtained by a specific process and has the two-dimensional and continuous pores (passages) is in conformity with the object of the present invention and on the basis of their findings, the present invention has been attained.